The present invention relates to an electromagnet for generating a static magnetic field to be used in a nuclear magnetic resonance apparatus.
The nuclear magnetic resonance apparatus has conventionally been widely used for analyzing the chemical structure of substances, particularly in recent days for imaging living bodies. As is well known, the static magnetic field used in this device must have very stable characteristics, and therefore the exciting current of the magnet needs to be made highly stable. In order to obtain such high stability of the exciting current, various kinds of feedback circuits associated with a current sensor have been provided. In this case, the current detecting sensor portion itself is so sensitive to the surrounding temperature that it needs to be placed in a temperature stabilized case. When the apparatus is not operated, the exciting current supply to the electromagnet is stopped to save power, and the heat generated in a current detecting circuit is very different between when the apparatus is on working and not on working. Such a temperature difference is compensated by the temperature stabilized case. This temperature compensation system has a problem, however, in that some medium put in the temperature stabilized case creates a time delay in the temperature compensation or a true temperature distribution cannot be obtained when the apparatus starts operating. Accordingly, it generally takes one hour or more after it is started for the apparatus to reach its stable operating state.